It is known in the art to increase the diffraction-limited power available from semiconductor optoelectronic devices to laterally taper or flare a portion of the device stripe region to the front or output facet of the device. By broadening the propagating beam through a tapered section that is electrically biased, the optical power can be increased while maintaining single mode operation of the device via the remaining portion of the stripe region which functions as a single mode filter. The single mode region may be pumped in combination with the tapered gain region forming what is termed an unstable oscillator. On the other hand, the single mode region may be fabricated to function as a laser oscillator and, as combined with the tapered gain region, forms a master oscillator power amplifier (MOPA) providing a stable resonator with an output beam that has lower divergence and much higher power levels compared to standard linear or straight stripe laser diodes. Examples of such unstable and stable resonators with tapered or flared gain regions are disclosed in U.S. Pat. Nos. 4,942,585; 5,537,432; 5,539,571; 5,392,308 and 5,592,503.
In these devices with an extended tapered gain region for propagating light amplification, the increase in optical output power is determined by the length and width of the tapered region, desired aperture width and the rate of free diffraction of the optical mode in the waveguide cavity leading to the tapered gain region. However, with an increase in output power comes the problem of catastrophic optical mirror damage (COD) particularly relative to the rear facet of such devices where the linear or straight single mode portion ends at the rear end facet of the device. Since the optical power of the device is significantly enhanced with the integrated tapered or flared gain portion of the optical waveguide cavity, COD can likely occur at the rear facet due to an increase in optical power density in such a small confined area or aperture.
Thus, it is a primary object of this invention to provide a means for maintaining the optical power density at the rear end facet of a semiconductor optoelectronic device at a level below that which leads to COD while retaining the single spatial mode filtering properties of the linear or straight single mode portion of the device.
It is also another primary object of this invention to provide a semiconductor optoelectronic device that includes at least one tapered region that is comparatively short in length compared to the total optical waveguide cavity providing at least a modest increase in optical output power above that of a standard single linear strip device having substantially the same cavity length so that the higher optical power performance device will fit into existing standard device packages designed for accommodating such standard linear stripe devices.
It is, therefore, an overall object of this invention to provide a semiconductor optoelectronic device that includes a strip pumping configuration that has one or more tapered or flared portions that improve device power output performance without COD or improve power capacity of the device, or both, without requiring additional dimensional length to the device optical cavity length so that such a modified device will fit in standard packages designed for conventional linear stripe devices.